In modern automobile automatic transmissions, hydraulically actuated clutches are used to change gears. In order for these shift operations to occur smoothly and unnoticed by the driver, it is necessary to adjust the hydraulic pressure on the clutches according to predefined pressure ramps with the maximum possible pressure precision. For this purpose, electromagnetically actuated pressure control valves are used. These may be configured as either seat valves or slide valves. Both configurations normally include three hydraulic connections, for intake, control pressure and return flow. In the case of slide valves, an axially displaceable control piston connects openings, for example, situated radially in a sliding sleeve, which are fluidically, in particular, hydraulically, connected, to an intake connection, to a control pressure connection and to a return flow connection. In this arrangement, the control pressure connection may be axially situated, for example, whereas the intake connection and the return flow connection are radially situated. In order to ensure the pressure regulating function of slide valves, it is necessary for the control piston to be able to carry out its axial movement largely undamped.
In particular, if the end faces of a control piston come into contact with hydraulic oil, the axial movement of the control piston may result in a so-called “pumping” of hydraulic oil through the control piston. Consequently, oil is displaced by the movement of the control piston or, in turn, oil is drawn in due to a resulting vacuum. Pressure control valves in automatic transmissions are normally installed in the hydraulic oil reservoir or in the so-called “oil sump” of the automatic transmission. During the operation of automatic transmissions, in particular, ferromagnetic particles form in conjunction with the friction of the transmission gears as a result of the abrasion of the gears. In the hydraulic oil reservoir, such ferromagnetic particles and other dirt particles may lead to functional impairments or malfunctions. Thus, for example, the guidance of the control piston or the electromagnetic actuation of the control piston may be adversely affected due to the contaminants. In particular, ferromagnetic particles may accumulate in this case in the area of the magnetic poles.
Various approaches are known for ensuring the pressure regulating function of slide valves and for minimizing the entry of dirt into a pressure control valve. A slide valve is believed to be understood from DE 10 2010 039 917 A1, whereby a push rod of the pressure control valve is sealingly, but axially displaceably, guided in a bearing bush. A slide valve, in which a diaphragm is provided between an actuating rod and the valve slide in order to ensure a flow medium sealing between two housing halves, is discussed in DE 103 25 070 A1.